1. Technical Field
This invention relates generally to procedures and equipment for hot tapping a pipeline, and more particularly to a valve assembly and hot-tapping method that provide increased component flexibility in addition to size, weight, and cost advantages.
2. Description of Related Art
“Hot tapping” refers to the procedures and equipment a worker employs to add a branch connection to an existing pipeline while the existing pipeline contains a fluid (often pressurized) without shutting down service. Any size and type of pipeline may be involved. To hot tap a line, the worker bolts or welds a fitting on a section of pipe in the line to form a tapping outlet structure (e.g., a flange). Next, he takes a conventional gate valve or other suitable hot-tapping valve and bolts the upstream end of the valve body on the tapping outlet.
Once the tapping valve is mounted on the pipe, he bolts a conventional hot-tapping machine to the downstream end of the valve body. The hot-tapping machine typically includes a motorized hole saw for sawing a hole in the pipe. After mounting it and pressure testing the hookup, the worker advances the hole saw through the body of the tapping valve with the valve-stopping element (i.e., the gate of the valve) in an open position. Next, he saws a hole in the wall of the pipe.
After forming the hole, the worker proceeds by retracting the hole saw sufficiently to close the valve-stopping element of the tapping valve. He closes it and then removes the tapping machine. That leaves the closed tapping valve connected to the pipeline and ready for service, and he may then connect a pipe, gauge, sensor, or other component to the downstream side of the valve body and open the valve when desired.
Hot tapping a line that way is well known. However, the size, weight, and expense of the gate valve employed can present problems, especially for 24-inch to 48-inch and larger pipelines. U.S. Pat. No. 5,660,199 addresses the problems with a hot-tapping method employing a valve that is similar in some respects to a conventional bonneted gate valve but which includes a bonnet isolating mechanism. After bolting the valve body to a hot-tapping outlet on the pipeline and then hot tapping the line through the valve body, the worker closes the valve, removes the hot-tapping machine, and connects a desired downstream component. Then, he completes the hot-tapping procedure recited in that patent by opening the valve to withdraw the gate fully into the bonnet, actuating the bonnet isolating mechanism to seal the valve body from the bonnet, and removing the bonnet from the valve body.
That way of doing it leaves just the smaller, lighter, and less expensive valve body connected to the pipeline, along with whatever downstream components are connected to the valve body. So, the hot-tapping procedure enables use of most any downstream component, including butterfly valves, globe valves, check valves, back flow preventers, gauges, sensors, and no-valve technologies. In addition, the larger, heavier, and more expensive bonnet is free for reuse elsewhere, and a bonnet can always be reattached to the valve body whenever desired in the future for pipeline servicing.
Although effective in many respects, the valve body cannot be re-isolated without reconnecting the bonnet and gate, and in many cases doing so requires excavation around the valve body. Moving the gate linearly in and out of the valve body requires significant space, especially for 24-inch to 48-inch and larger pipelines. Thus, a need exists for a better way for hot tapping an existing pipeline.